According To Acts Of The Apostles On Which Holy Day Did The Holy Spirit Descend?

The Holy Spirit came on Shavuot. Shavuot is one of the the Jewish pilgrimage festivals, and is also known as the "Feast of Weeks". Greek Speaking Jews gave it the name Pentecost because it occurs exactly 50 days after Passover. The observance of Pentecost (Shavuot) included the offering of two loaves of unleavened bread, as the "first fruits" of the harvest. For Christians, Jesus became the first fruits of the harvest of God.
"When the day of Pentecost came, they were all together in one place. Suddenly a sound like the blowing of a violent wind came from heaven and filled the whole house where they were sitting. They saw what seemed to be tongues of fire that separated and came to rest on each of them. All of them were filled with the Holy Spirit and began to speak in other tongue as the Spirit enabled them." (Acts 2:1-2)

Pentecost

The Pentecost